1. Field of the Invention
The present invention relates to a process and apparatus for producing fibers by a centrifugal spinning process.
2. Description of the Prior Art
Various ways are known for producing fibers, in particular from amino resins.
GB-A-1 141 201 describes the production of fibers starting from a resin material which is introduced between surfaces of a pair of belts. The belt surfaces are then moved apart, which results in fibers being formed.
DE-A-2 364 091 describes a process for producing flame-resistant and thermally unmeltable melamine resin fibers wherein a solution of a melamine-aldehyde precondensate is spun into a heated atmosphere, evaporating the solvent and curing the precondensate.
DE-A-2 810 535 describes a process for producing fibers from a heat-curable formaldehyde resin by centrifugal spinning, wherein the fibers are formed cocurrently with cold, moist air. For this a stream of cold, moist air is deflected downward in the direction of the whirler drum in such a way that at least part of this air stream enters the whirler drum together with the mixture of resin and catalyst, so that the air stream counteracts any drying-out and reaction of the mixture as long as the latter is present in the whirler drum or plate. The fibers emerging from the whirler drum are entrained and attenuated by the cold, moist air stream. The attenuated fibers are then heated to 50.degree.-100.degree. C. and collected by a stream of hot, dry air flowing from underneath the whirler drum toward the outside.
These processes have a number of disadvantages. In some instances the spinning solutions have to have a very low viscosity. This produces very brittle, short fibers which cannot be used for web or fabric production. If, on the other hand, high viscosity solutions are used and spun at higher temperatures, it is found that the fiber-forming step is accompanied by considerable inter-fiber fusion and that the danger of jet collapse is considerable.
The process of DE-A-2 810 535, where cold, moist air is used, likewise gives rise to considerable inter-fiber fusion because of the long residence time in a moist atmosphere prior to drying. The fiber bundles are impossible to separate and lead to brittle, friable, thick fibers which are very difficult to process into webs and yarns.
In existing processes the fibers are formed from partly filled nozzles, i.e. the stream of resin from which the fibers are formed does not fill out the entire nozzle cross section as the fibers are being spun.